The purpose of this research was to measure the copper-binding behavior of Dissolved Organic Matter (DOM) contained in Pulp and Paper (P&P) wastewater effluent and evaluate the Biotic Ligand Model’s (BLM) ability to quantify copper speciation in P&P influenced waters. A copper ion selective electrode was used to measure copper activity in four P&P mill effluents and their receiving waters with the purpose of quantifying metal binding behavior with a two-site ligand model. In addition, USGS flow data and the optical properties of DOM were used to evaluate the relative contribution of P&P organic material to each river system studied and the ability of the specific UV absorbance at 254 nm (SUVA254) to predict metal-binding behavior.
Experimentally measured copper-ligand affinity and site-density parameters were used to develop a site-specific copper-speciation model in the chemical equilibrium software program Visual MINTEQ for comparison to the BLM. Results indicate P&P effluent DOM has a greater strong-ligand site density and SUVA254 in comparison to receiving waters, but the ability to detect the influence of these characteristics downstream was limited by the high dilution ratios and uncertainty of accounting for all inputs to the river system. While SUVA254 was poorly correlated with metal-binding when analyzing data from all sites, there was a strong, positive correlation between the variables at two sites, and therefore more work is needed to determine if SUVA254 can be used to predict metal-binding behavior. Regarding simulation results, the BLM and MINTEQ models were consistently within an order of magnitude, but the BLM regularly predicted less available copper at environmentally relevant concentrations. Diluted effluent sample simulations were in better agreement (within 2-3x) at environmentally relevant total copper concentrations (5-15 µg/L) than their corresponding upstream and downstream counterparts, an indication of more copper-binding potential in the effluent samples that isn’t accounted for in the BLM. In contrast, the BLM predicted up to 5x more bioavailable copper at lower total copper concentrations in one fully concentrated (7.23 mg/L DOC) effluent sample, indicating the BLM may not properly quantify low-level copper availability in concentrated, P&P wastewater effluent. Thus, while the BLM is a useful tool for predicting copper speciation, the model may be improved by allowing researchers to specify more detailed binding characteristics of DOM, especially when evaluating P&P influenced waters.